Longitudinal shaft

ABSTRACT

The invention concerns a longitudinal shaft  1 , for use in particular in four-wheel drive or rear-wheel drive motor vehicles. The longitudinal shaft  1  comprises a gearbox-side articulation  5 , a differential-side articulation  6 , as well as a central articulation  4  through which a gearbox-side section  2  is integrally linked in rotation to a differential-side section  3  of the longitudinal shaft  1 . The invention aims at reducing the centrifugal forces occurring at the longitudinal shaft  1  in operation. Therefor, the gearbox-side articulation  5  and the differential-side articulation  6  have each an inner hub  15, 18  designed to connect the longitudinal shaft  1  integrally in rotation respectively to a gearbox output shaft and to a differential input shaft, the longitudinal shaft  1  being centered on the gearbox output shaft and the differential input shaft by interlocking through the inner hubs  15, 18.

The invention relates to a longitudinal shaft, particularly for use inautomobiles having all-wheel drive or rear-wheel drive, comprising agearbox-side articulation, a differential-side articulation, and acentral articulation, each of which have an inner hub and an outer hubthat surrounds the former at least in some regions, whereby two shaftsegments are connected with one another so as to rotate together, by wayof the central articulation. In this connection, the terms“gearbox-side” and “differential-side” are used merely as examples inthe sense of this invention, to differentiate the two ends of thelongitudinal shaft.

In the case of automobiles, which usually have a motor with atransmission, installed in the front in the direction of travel, thedrive torque of the engine is transferred to the rear axle differentialfor rear-wheel drive, by way of a longitudinal shaft disposed in thedirection of travel. In this connection, the longitudinal shaft issubjected to stresses that are as high as ten times the rated torque, asthe result of frequently changing torques and speeds of rotation, aswell as load shocks. At the same time, the vibrations and noisesproduced by the longitudinal shaft are supposed to be kept as low aspossible.

Usually, a longitudinal shaft of the type stated initially is attachedto the transmission output shaft and the differential input shaft,respectively, by way of a flange connection with the outer rings of thegearbox-side articulation and of the differential-side articulation.This flange connection simultaneously serves to center the longitudinalshaft. However, in the case of the high speeds of rotation of thelongitudinal shaft that frequently occur during operation, between 8,000and 10,000 revolutions per minute, even slight balance errors of thelongitudinal shaft resulting from insufficient centering will bringabout great centripetal forces in the longitudinal shaft, which resultin vibrations and disruptive noises.

It is therefore the task of the invention to make available alongitudinal shaft of the type stated initially, in which thecentripetal forces that cause the vibrations and noises are reduced tothe greatest possible extent.

This task is accomplished, according to the invention, in that the innerhubs of the gearbox-side articulation as well as of thedifferential-side articulation have a central bore provided with aplug-in tooth system, to connect the longitudinal shaft for integralrotation, and to center it, on journals of a gearbox output shaft and adifferential input shaft, respectively. In this connection, theinvention is based on the idea that the centering diameter of a plug-inconnection between the inner hub of the gearbox-side articulation and ofthe differential-side articulation with the gearbox output shaft and thedifferential input shaft, respectively, which diameter is clearlysmaller as compared with flange centering, allows a significantreduction in the unbalance of the longitudinal shaft, at the samequality of tolerance. In this manner, the centripetal forces caused bythe unbalance are also reduced, thereby increasing the comfort of thevehicle, by means of lower vibrations and noises of the drive train. Theconnection between the gearbox output shaft and the differential inputshaft by means of the longitudinal shaft takes place, in thisconnection, in that the profiled inner hub of the gearbox-sidearticulation of the longitudinal shaft is set onto a correspondinglyprofiled journal of the gearbox output shaft, and the inner hub of thedifferential-side articulation is pushed onto a journal of thedifferential input shaft. In this manner, not only is a connectionbetween the gearbox output shaft and the differential input shaft thatpermits integral rotation produced, but also centering of thelongitudinal shaft is achieved.

The centering of the two segments of the longitudinal shaft by way ofthe central articulation can be improved if the central articulationalso has an inner hub having a central bore that is provided with aplug-in tooth system, which accommodates a corresponding journal of ashaft segment of the longitudinal shaft for plug-in centering forintegral rotation. Here, the connection between the two segments of thelongitudinal shaft in the central articulation takes place inessentially the same manner as the connection of the gearbox outputshaft and the differential input shaft to the longitudinal shaft.

In a further development of the idea of the invention, it is providedthat the two shaft segments of the longitudinal shaft are configured asshaft tubes, and the outer hubs of the gearbox-side articulation, thedifferential-side articulation, and the central articulation are shapedsheet-metal parts directly connected with the shaft tubes. The greatestpossible use of shaped sheet-metal parts in the articulations of thelongitudinal shaft, which are connected directly to the longitudinalshaft tubes by way of a weld seam, for example, reduce the overallweight of the longitudinal shaft. Minimization of the weight of thelongitudinal shaft also contributes to reducing the centripetal forcesthat occur, along with the improved centering.

In the gearbox-side articulation, as well as in the centralarticulation, only very slight angles of inclination usually occurduring operation, so that the use of a synchronous articulation in thegearbox-side articulation or the central articulation of thelongitudinal shaft would not result in any clear improvement of thesynchronicity properties. In order to achieve optimal efficiency of thelongitudinal shaft according to the invention, it is therefore preferredto implement the gearbox-side articulation and/or the centralarticulation as a sliding articulation.

If the gearbox-side articulation and the central articulation areconfigured as sliding articulations and have a commoninstallation/displacement path, which corresponds at least to a lengthsuch that the gearbox output shaft or the differential input shaftprojects into the inner hub of the gearbox-side articulation or thedifferential-side articulation, respectively, in operation, thelongitudinal shaft according to the invention can be installed inparticularly simple manner, between the gearbox output shaft and thedifferential input shaft.

Since the angles of inclination during operation of thedifferential-side articulation of the longitudinal shaft usually lie ina range that lies clearly above those of the gearbox-side articulationand the central articulation, it is preferred, in order to improve thesynchronicity properties, to configure the differential-sidearticulation as a synchronous articulation.

According to a preferred embodiment of the invention, the gearbox sideshaft segment of the longitudinal shaft has a diameter that differs fromthat of the differential-side shaft segment, in such manner that the twoshaft segments can be pushed onto one another in the manner of atelescope. With this embodiment of the longitudinal shaft, it is avoidedthat the longitudinal shaft will bend out when compressed end to end,for example as the result of an accident, and penetrate into thepassenger compartment of the vehicle. Instead, if in-line compressionoccurs, the two shaft segments of the longitudinal shaft will move intoone another in the manner of a telescope, so that danger to thepassengers in the passenger compartment of the vehicle, resulting fromthe longitudinal shaft, is reduced.

The invention will be explained in greater detail in the following onthe basis of an exemplary embodiment, making reference to the drawing.

This shows:

FIG. 1 a longitudinal shaft according to the invention, incross-section, and

FIG. 2 a detail view of the gearbox-side articulation.

The longitudinal shaft 1 shown in FIG. 1 has two shaft segments 2 and 3,configured as shaft tubes, which are connected with one another by meansof a central articulation 4. The left end of the longitudinal shaft 1 inthe figure is the gearbox side that is usually disposed at the front ofa vehicle in the direction of travel, while the right end of thelongitudinal shaft 1 in the figure faces a rear axle differential in theinstalled state.

The gearbox-side shaft segment 2 of the longitudinal shaft 1 ends, onits side facing away from the central articulation 4, in a gearbox-sidearticulation 5, while the second shaft segment 3 has a differential-sidearticulation 6 at its end facing away from the central articulation 4.The shaft segments 2 and 3 are configured as sheet-metal tubes, wherebythe tube that forms the gearbox-side shaft segment 2 of the longitudinalshaft 1 is connected with the outer hub 7 of the gearbox-sidearticulation 5, which hub is configured as a shaped sheet-metal part, byway of a weld seam 8, and is welded to a hollow shaft journal 9 on itsside facing the central articulation 4. The tube that forms thedifferential-side shaft segment 3 of the longitudinal shaft 1 isconnected with the outer hub 11 of the central articulation 4, or theouter hub 12 of the differential-side articulation 6, respectively,which are both configured as shaped sheet-metal parts, by way of weldseams 10 a and 10 b, respectively.

The outside diameter D₂ of the gearbox-side shaft segment 2 of thelongitudinal shaft 1 is somewhat smaller than the inside diameter D₃ ofthe differential-side shaft segment 3 of the longitudinal shaft 1, sothat the two shaft segments 2 and 3 can be pushed into one another inthe manner of a telescope.

The gearbox-side articulation 5 as well as the central articulation 4are sliding articulations, which have, from the outside to the inside,the outer hub 7 or 11, respectively, a cage 13, in which several balls14 are guided, and an inner hub 15. In this connection, the inner hub isprovided with a central bore 16 that has a plug-in tooth system 17 foran integral rotation connection and centering with a correspondinglyprofiled journal.

On the outside of the inner hub 15 and the inside of the outer hub 7 or11, ball raceways that run in the axial direction of the longitudinalshaft 1 are formed, in which the balls 14 guided by the cage 13 can rollor slide, in order to allow an axial displacement between the outer hub7 or 12 and the inner hub 15. In this connection, as shown in FIG. 2,the cage 13 can be guided to be axially displaceable in the inner hub15, or can have a cage guide in the outer hub (not shown).

The differential-side articulation 6 of the longitudinal shaft 1 isstructured as a counter-path synchronous articulation having a profiledinner hub 18, a cage 20 that guides several balls 19, and the outer hub12 provided with an insert 21. In this connection, a central bore 22having a plug-in tooth system 23 for integral rotation accommodation andcentering of a correspondingly profiled journal 24 of a differentialinput shaft is provided in the inner hub 18.

The journal 9 that is connected with the gearbox-side segment 2 of thelongitudinal shaft 1 is elastically mounted by way of a ball bearingunit 25. Furthermore, the longitudinal shaft 1 is centered and mountedby means of the gearbox-side and differential-side articulations 5 and6, respectively, in the inside hubs 15 and 18.

Installation of the longitudinal shaft 1 between the journal of agearbox output shaft (not shown) and the journal 24 of a differentialinput shaft takes place, for example, in that first, the inside hub 15of the gearbox-side articulation 5 is set onto the corresponding journalof the gearbox output shaft. The gearbox-side articulation 5 as well asthe central articulation 4, which are both configured as slidingarticulations, can be axially displaced from their center operatingposition of the balls 14, shown in FIG. 2, in both directions, by thelength l₁, before the balls 14 reach the delimitation predetermined bythe outer hub 7 or 11, which delimitations are indicated by the dot-dashlines 14 a and 14 b. In every sliding articulation, the inner hub can bedeflected in both directions, by the length l₁, relative to the outerhub, from the position shown in FIG. 2, while the balls 14 are rolling.

In addition, the inner hub 15 can be displaced relative to the outer hub7 or 11, by the length l₂, on the inner hub 15, while the balls 14 arerolling, when the balls rest against the delimitation stop 26 connectedwith the outer hub. In this connection, the maximal movement of theballs 14 on the inner hub 15 is limited by means of split rings 27.

The assembly displacement path of the gearbox-side articulation 5 aswell as of the central articulation 4, which is composed of the lengthsl₁+l₂, in each instance, corresponds to at least half of the length L,with which the journal 24 of the differential input shaft projects intothe inner hub 18 of the differential-side articulation 6 in operation.The longitudinal shaft 1 can thereby be pushed into itself, in thegearbox-side articulation 5 and the central articulation 4, to such anextent that the inner hub 18 of the differential-side articulation 6 canbe oriented in alignment with the journal 24 of the differential inputshaft. By means of displacing the inner hubs 15 relative to the outerhubs 7 and 11 in the gearbox-side articulation 5 and the centralarticulation 4, the inner hub 18 of the differential-side articulation 6is pushed onto the journal 24 of the differential input shaft. When thisis done, the longitudinal shaft 1 is simultaneously centered with thedifferential input shaft.

The articulations 4, 5, and 6 of the longitudinal shaft 1 canfurthermore be sealed and protected against the penetration of dirt, bymeans of protective sheet metal pieces 28 a, 28 b, and 28 c, as well asby means of folded bellows 29 a, 29 b, and 29 c.

1. Longitudinal shaft, particularly for use in automobiles havingall-wheel drive or rear-wheel drive, comprising a gearbox-sidearticulation (5), a differential-side articulation (6), and a centralarticulation (4), each of which has an inner hub (15, 18) and an outerhub (7, 11, 12) that surrounds the former at least in some regions,whereby two shaft segments (2, 3) of the longitudinal shaft (1) areconnected with one another so as to rotate together, by way of thecentral articulation (4), wherein the inner hubs (15, 18) of thegearbox-side articulation (5) as well as of the differential-sidearticulation (6) have a central bore (16, 22) provided with a plug-inconnection (17, 23), to connect the longitudinal shaft (1) for integralrotation, and to center it, on journals (24) of a gearbox output shaftand a differential input shaft, respectively.
 2. Longitudinal shaft asrecited in claim 1, wherein the central articulation (4) has an innerhub (15) having a central bore (16) that is provided with a plug-intooth system (17), which accommodates a journal (9) of a shaft segment(2) of the longitudinal shaft (1) for plug-in centering for integralrotation.
 3. Longitudinal shaft as recited in claim 1, wherein the twoshaft segments (2, 3) of the longitudinal shaft (1) are configured asshaft tubes, and the outer hubs (7, 11, 12) of the gearbox-sidearticulation (5), the differential-side articulation (6), and thecentral articulation (4) are shaped sheet-metal parts directly connectedwith the shaft tubes.
 4. Longitudinal shaft as recited in claim 1,wherein the gearbox-side articulation (5) and/or the centralarticulation (4) are sliding articulations.
 5. Longitudinal shaft asrecited in claim 4, wherein the sliding articulations (4, 5) togetherhave an assembly displacement path (2 l₁+2 l₂), which corresponds to atleast a length (L), with which the gearbox output shaft or thedifferential input shaft (24) projects into the inner hub (15, 18) ofthe gearbox-side articulation (5) or the differential-side articulation(6) in operation.
 6. Longitudinal shaft as recited in claim 1, whereinthe differential-side articulation (6) is a synchronous articulation. 7.Longitudinal shaft as recited in claim 1, wherein the gearbox-side shaftsegment (2) has a diameter (D₂) that deviates from diameter (D₃) of thedifferential-side shaft segment (3), in such a manner that the two shaftsegments (2, 3) of the longitudinal shaft (1) can be pushed onto oneanother in the manner of a telescope.